Why did the salmon turn brown when I steamed it

That white stuff is albumen, the same protein that makes the white of chicken eggs. The albumen is part of the salmon's blood, which means that your fillet was fresh. A trick for dealing with it was developed by Bruno Goussault while collaborating with chef Michel Richard from Citronelle in DC: soak the salmon pieces in an ice cold brine. The article in the New York Times that told the story recommends soaking the salmon fillets for ten minutes in a 10% brine (by weight). To make the brine, dissolve three tablespoons of Kosher salt for every cup of ice cold water and make as many cups as you need.

It boils down to chemical make up. Avocados, like egg yolks, contain a decent amount of fats, carotenoids, and sulfurous compounds. Avocados are one of the most concentrated fruit sources of fats and fatty acids. Both egg yolks and avocados contain carotenoid phytochemicals like lutein, zeaxathanin, and a-carotene. In avocados the sulphur is mostly in the form of glutathione, would likely break down into its cysteine during steaming. Cysteine is one of the primary sulphur sources in eggs as well.

• http://www.avocado.org/new-research-from-ucla-shows-california-avocados-contribute-additional-beneficial-carotenoids-2